Foil bearing stiffener

ABSTRACT

An improved stiffener element for use in foil journal bearings provides damping of eccentric shaft rotation in both bending and compression modes of operation and also provide greater load capacity and higher speeds for the bearing.

This invention relates generally to self-pressurizing hydrodynamicbearings for providing fluid support between two members movablerelative to each other and supported on a thin fluid film. Moreparticularly the invention relates to bending foil type fluid bearingsin which means are provided for stiffening the foils to enhance the loadcarrying capability of the bearing and to provide dampening andcushioning effects between the two members. A detailed backgrounddescription of self-pressurizing foil bearings is disclosed in U.S. Pat.No. 3,635,534 entitled "Self-Pressurizing Bearings with ResilientElements."

In resilient foil bearings of this type, the principle difficulties havebeen limited foil stiffness and oscillatory motions between the movableand stationary member at certain critical bearing speeds. It is ageneral advantage of foil bearings to have the foil of thin material inorder that it may conform to the supported member more uniformly underall conditions. However, the thinner foil is more compliant and thus hasa reduced load bearing capacity. In the case of the second problem, dueto unbalance, the shaft in a high speed bearing for rotating machinestends to orbit about the geometric center of the bearing support and theamplitude of the oscillation is maximized at certain critical speeds. Inorder to control this oscillation, it is desirable to have a substantialamount of damping in the bearing assembly.

The present invention overcomes these difficulties by providing aresilient foil support disposed beneath each of the primary foils and incontact with the primary foil intermediate its ends. This has the effectof increasing the total foil stiffness. At the same time, the primaryfoil may be made of relatively thin material over its entire length sothat it will easily conform to the shape of its matching member toprovide the optimum fluid bearing under normal operating conditions. Toresist oscillation of the bearing shaft at certain critical speeds, thefoil supports are so arranged that the primary foil tends to rub alongthe stiffening member during oscillatory motions in a first operativeconfiguration. This rubbing action produces Coulomb friction which aidsin damping the vibration of the shaft.

Should this oscillatory motion of the shaft or side load become so greatthat the foils and stiffening elements bend a sufficient amount toconform to the shape of the carrier ring, the stiffener is compressiblein a second operative configuration to provide additional film clearanceat a higher spring rate. In this manner, greater load capacity isprovided and higher bearing speeds may be obtained without shaft runoutcausing "bottoming" of the bearing.

The advantages of the improved bearing arrangements of this inventionwill be more readily understood when the following specification is readin conjunction with the appended drawings, wherein:

FIG. 1 is a longitudinal sectional view through a bearing of thisinvention;

FIG. 2 is a partial sectional view of the bearing of FIG. 1;

FIG. 3 is a view of the bearing of FIG. 1 including a rotating shaft;

FIG. 4 is an enlarged section of a portion of FIG. 3;

FIG. 5 is a sectional view of a stiffening member of this invention;

FIG. 6 is a perspective view of the stiffening member of FIG. 5;

FIG. 7 illustrates an alternate embodiment wherein the stiffening memberis combined with a foil member in a single structure;

FIG. 8 illustrates an alternative bearing construction for use of astiffening member in accordance with this invention; and

FIG. 9 illustrates a foil bearing element of this invention for use in aconical foil bearing.

Referring now to the drawings, FIGS. 1 and 3 illustrate a bearingassembly 10 interacting with a portion of a rotating shaft 12 to serveas bearing members or bearing elements for supporting the rotating shaft12. The bearing assembly generally comprises a bearing housing ring 14supporting a concentric foil carrier ring 16. The carrier ring isprovided with axial slots 18 which provide passages for cooling airalong the axis of the bearing and also provide for axial pressurebalancing of the bearing. One of these slots is used in connection witha pin 20 to prevent relative rotation between the housing 14 and thefoil carrier 16. The pin 20 extends through the housing member andpartially into one of the passages 18 to provide a locking function.

Attached to the inner surface of the carrier ring 16 are a plurality offoils 22 which are seated in axial slots 24 in the carrier ring 16 andretained in the slot by slugs 26. Also held in the slots 24 by the slugs26 are a plurality of foil support members 28.

As can be seen in FIG. 1, both the foils 22 and foil support members 28are given an initial curvature larger than that of the shaft 12 and thusprovide a pre-loading of the bearing. After the shaft 12 has beeninserted, as shown in FIG. 3, bending the foils 22 and supports 28 causethe curvature to more closely approach each other. However, it will bereadily understood that oscillation of the shaft will cause somewhatdifferent relative rates of deformation of the foils 22 and foil supportmembers 28 which will cause the free end of the support members to rubon the associated outer surface of the foils 22. This rubbing actionwill generate Coulomb friction and will aid in damping the oscillationof the shaft.

Damping of the oscillations of the shaft is also provided by the bendingaction of the foils 22, largely aided by the bending of the foil supportmembers 28 along therewith. This action is described in detail in theaforementioned U.S. Pat. No. 3,635,534 and in U.S. Pat. No. 3,893,733entitled "Foil Bearing Arrangements". As is described in these patents,interaction of the rotating shaft 12 and the bearing foils 22 causes alayer of air to form therebetween supporting the shaft. Supporting theshaft within this layer of air causes a very low friction bearing to beformed.

Increases in the load to be supported by the bearing or in the speed ofrotation of the shaft 12 tends to cause increased shaft run out, acondition wherein the shaft approaches more closely the inner surface ofthe foil carrier ring 16. This motion of the shaft 12 applies forcethrough the layer of air against the foils 22 which bend in responsethereto and rub on each other resulting in a damping of thisoscillation, the amount of damping being partly dependent upon thebending spring rate or stiffness of the foil and partly on the frictionforces. Thus, by making a stiffer and more damped foil, shaft run outcan be more readily controlled without danger that the foil will become"grounded" or flattened against the foil carrier ring so that it is nolonger able to respond to the oscillations and damp the motion of theshaft.

Generally, it is desirable to make the foils of relatively thin materialto more readily conform to the shape of the shaft and optimize bearingoperation. Thus, foil support members or stiffeners have been utilizedto provide the higher bending spring rate while permitting the foilitself to be thin.

However, for larger loads or higher operating speeds, the radialdisplacement may still become so great that the foil 22 and supportmember 28 become flattened against the inner surface of the foil carrierring 16. With prior art bearings, operation under such conditions wouldprevent further yielding of either the foil or support member and causeloss of the air film. Thus, further damping action in response toincreased oscillation could not occur and foil and stiffener are"grounded". Any increase in oscillation of the shaft will cause hardimpact against the carrier ring which may be highly damaging or, at thevery least, will significantly slow shaft rotation.

The foil support member 28 of this invention provides significantimprovement over prior art devices in that it is capable of providinglocal support and shaft damping even under conditions in which prior artstiffeners would have become grounded and unable to functionefficiently. The foil support member 28 is best illustrated in FIGS. 5and 6 and is preferably formed of metallic foil bent to form a foilsupport mounting portion 32 at one end thereof. The foil support member28 is bent to a predetermined curvature, larger than the curvature ofthe foil carrier ring 16 or shaft 12 (see FIG. 1) so as to provide apreloading of the bearing as previously discussed. This curvatureshould, however, preferably not substantially differ from the curvatureof the foils 22.

The convex under surface of support member 28 is preferably etched orgrooved to alternately provide flat topped ridges 34 and groove 36. Thetop surface is also provided with alternate ridges 38 and grooves 40.The grooves 36 and 40 provide useful cooling to the bearings bydirecting the flow of fluid along the length of the foil. The ridges 34and 38 are generally flat topped so as to facilitate sliding of thefoils thereover and also to minimize waviness in the fluid film surface.

In order to provide a resilient or spring-like structure, the uppersurface ridges 38 are opposed to the lower surface grooves 36 while theupper surface grooves 40 are opposed to the lower surface ridges 34.While the grooves and ridges can be accurately and cheaply produced byphotochemical etching or machining techniques, alternative methods, suchas bonding a plurality of narrow strips to the foil surfaces, may beutilized.

Referring now to FIG. 4, the substantial advantages of the specificconfiguration of the foil support member 28 of this invention can beseen. In FIG. 4, the bearing is represented in a configuration where,under the influence of either a large load or a high rotational speed ora combination thereof, oscillatory run out of the shaft 12 has increasedto such a degree that the foils 22 and foil support members 28 areforced against the foil carrier ring 16 by the action of the rotatingshaft 12. In this configuration, damping can no longer be provided byeither the bending action of the foil 22 and foil support member 28 orby the Coulomb friction resulting from interaction of the members. Werea prior art stiffener used under these conditions, the bearing would begrounded.

However, with the foil support member 28 of this invention, the foil 22is pressed against the ridges 38 on the top surface of the supportmember while the ridges 34 on the under surface of the support memberrest against the foil carrier ring 16. The application of furtherpressure by the fluid layer between the shaft 12 and foil 22 causes thefoil support member to yield in a compression mode so that damping andfluid film clearance continues and bearing operation is not degraded. Aswill be readily understood, this compression of the support member 28has a significantly higher "spring rate" than is exhibited by thesupport member when yielding in a bending mode. Thus, effective dampingcan be provided by the support member which will permit the bearingsupport much greater loads than could be tolerated by bearings utilizingprior art stiffeners.

In our U.S. Patent Application Ser. No. 689,619, filed concurrentlyherewith, a novel foil bearing structure is illustrated whereinindividual compliant foils are mounted intermediate the ends thereof.The use of the foil support member of this invention in such a structureis illustrated in FIG. 8. As described in more detail in theaforementioned application Ser. No. 689,619, each foil bearing element50 comprises a thin compliant bearing foil 52 having a mounting bar orrod 54 affixed intermediate the ends thereof, for example by spotwelding. A plurality of foil bearing elements 50 are adapted to beplaced around the interior of a bushing 56 with the mounting bars 54adapted to fit in grooves or slots 58 in the inner surface of thebushing.

Each bearing foil 52 includes an over foil 60 and an under foil 62 oneither side of the mounting bar 54. The under foil 62 on one side of themounting bar 54 is adapted to be positioned under the over foil 60 onthe other side of the mounting bar 54 of the next adjacent bearing foil52.

When a shaft 66 is inserted into the bushing 56, the compliant bearingfoils 52 are compressed into the space between the shaft 66 and bushing56 such that the under foil 62 provides a resilient support for the overfoil 60 of the next adjacent bearing foil 52. The mounting bars 54 arealso forced more deeply into the grooves 58 at the inner surface of thebushing 56. Each foil 52 acts as a flexible beam pivoting on andsupported at the end of the under foil 62 by an inner surface 64 ofbushing 56 and at the free end of the over foil 60 by the next adjacentbearing foil 52. Under load, the individual bearing foils 52 tend tobend between the support points. The end of the under foil 62 will tendto slide on the inner surface 64 of the bushing 56 while the free end ofthe over foil 62 will slide over the next adjacent bearing foil 52.Movement of the bearing foils 52 will, however, be limited by themounting bar 54 in the slot 58.

A foil support member 28A, similar to the foil support member 28 ofFIGS. 5 and 6 may be utilized to provide stiffening for the under foil62 in this bearing arrangement. The substantial difference between foilsupport members 28A and 28 lies in the length of the foil support member28A being substantially co-extensive with the under foil 62 of the foilbearing element 50 so that contact with the surface 64 is actually withthe end of the foil support member 28A. As in the foil bearingarrangement of FIG. 3, the foil support member 28A permits lighter, moreflexible longer foils to be used for providing ideal fluid film shapefor the bearing to optimize bearing performance while providing enhancedstiffening and damping operation by functioning initially in a bendingmode and when bending is no longer possible functioning in asubstantially purely compressive mode.

An alternative foil bearing element 70 is illustrated in FIG. 7 andincludes a bearing foil 72 affixed to a mounting bar 74. On one side ofthe mounting bar 74 is a bearing foil portion 76. On the other side ofthe mounting bar 74 is a foil support portion 78. The under surface ofthe foil support portion 78 is preferably etched or grooved toalternately provide flat topped ridges 80 and grooves 82 and the topsurface is also provided with alternate ridges 84 and grooves 86, theridges 84 on the upper surface being spaced between the ridges 80 on thelower surface. By substituting the foil bearing element 70 for the foilbearing element 50 of FIG. 8, the desired stiffening and dampingcharacteristic can be provided for the bearing without the need for anyadditional foil support member.

It will be readily apparent that the foil support members made inaccordance with this invention may be utilized in various bearingconfigurations either integrally formed with or separate from the foilbearing elements. FIG. 9 illustrates a foil bearing element 90 for aconical foil bearing having a bearing foil portion 92 and a foil supportportion 94. Foil support portion 94 is provided with ridges 96 on itsouter surfaces and ridges 98 on its top surface which alternate with theridges 96 to provide the compressibility provided by foil supportmembers in accordance with this invention.

While specific embodiments of the invention have been illustrated anddescribed, it is to be understood that these are provided by way ofexample only and that the invention is not to be construed as beinglimited thereto but only the proper scope of the following claims.

We claim:
 1. A hydrodynamic fluid bearing comprising:first and secondbearing elements movable with respect to each other and spaced apart toform a fluid gap therebetween; at least one bearing foil attached to oneof said bearing elements, said foil loosely conforming to the shape ofsaid bearing elements; foil stiffening means operatively associated withone of said bearing members and contacting said bearing foil at least atone point for increasing the effective stiffness of said bearing foil,said foil stiffening means having a first operative configuration forproviding damping by bending and a second operative configuration forproviding damping by compression.
 2. A hydrodynamic fluid bearing as inclaim 1 wherein said foil stiffening means comprises a resilient foilmember having alternating raised portions on inner and outer surfacesthereof.
 3. A hydrodynamic fluid bearing as in claim 1 wherein said foilstiffening element comprises:a compliant foil element having inner andouter surfaces; alternating ridge and groove means along the innersurface; and alternating ridge and groove means along the outer surface,each outer surface ridge means positionally corresponding to an innersurface groove means.
 4. A hydrodynamic fluid bearing as in claim 1wherein said bearing foil comprises:mounting means; a compliant foilelement extending from said mounting means in one direction; and saidfoil stiffening means extending from said mounting means in anotherdirection.
 5. A hydrodynamic fluid bearing as in claim 4 wherein saidfoil stiffening element comprises:a compliant foil element extendingfrom said mounting means in said other direction, and having inner andouter surfaces; ridge and groove means along the inner surface; andridge and groove means along the outer surface positionally alternatingwith said inner surface ridge and groove means.
 6. In combination:a pairof members arranged for relative rotation with respect to one another,one of said pair of members adapted to rotatively support the other; acompliant foil bearing operably disposed between said pair of relativelyrotatable members, said compliant foil bearing comprising a plurality ofoverlapping compliant foils and means for mounting said foils on one ofsaid pair of members; and foil stiffening means mounted on said one ofsaid pair of members for increasing the effective stiffness of saidfoils and having a first operative configuration for providing dampingby bending and a second operative configuration for providing damping bycompression.
 7. The combination of claim 6 wherein said foil stiffeningmeans comprises a foil stiffening member operably associated with eachof said foils and comprising:a compliant foil element having inner andouter surfaces; a plurality of protrusions along said inner surface; anda plurality of protrusions along said outer surface alternatingpositionally with said plurality of inner surface protrusions.
 8. Thecombination of claim 7 including an elongated mounting portion formounting on said one of said pair of members, and wherein saidprotrusions are aligned generally parallel with said mounting portion.9. The combination of claim 6 wherein said foil stiffening meanscomprises a foil stiffening member operably associated with each of saidfoils and comprising:a compliant foil element having inner and outersurfaces; a plurality of depressions along said inner surface; and aplurality of depressions along said outer surface alternatingpositionally with said plurality of inner surface depressions.
 10. Thecombination of claim 9 including an elongated mounting portion formounting on said one of said pair of members, and wherein saiddepressions are aligned generally parallel with said mounting portion.11. The combination of claim 6 wherein said foil bearing comprises ajournal bearing.
 12. The combination of claim 6 wherein said foilbearing comprises a conical bearing.
 13. A foil stiffening element foruse in a foil bearing system, said foil stiffening element comprising:acompliant foil element having inner and outer surfaces; a plurality ofalternating ridges and grooves along the inner surface; and alternatingridges and grooves along the outer surface, each outer surface ridgepositionally corresponding to an inner surface groove.
 14. A foilstiffening element as in claim 13 wherein each of said ridges is flattopped.
 15. A foil stiffening element as in claim 13 wherein saidcompliant foil element is generally arcuate.
 16. A foil stiffeningelement as in claim 13 wherein said foil element extends from mountingmeans in one direction and said ridges and grooves are generallyparallel to said mounting means.
 17. A foil stiffening element as inclaim 16 wherein an additional compliant foil element extends in anotherdirection from said mounting means.
 18. A foil stiffening element foruse in a foil bearing system, said foil stiffening element comprising:acompliant foil element having first and second surfaces; ridge andgroove means along said first surface; and ridge and groove means alongsaid second surface alternating with said first surface ridge and groovemeans.
 19. A foil stiffening element as in claim 18 having mountingmeans intermediate the ends thereof and wherein said ridge and groovemeans are positioned toward one of said ends from said mounting means.20. A foil stiffening element comprising:a compliant foil element, afirst surface on said foil element having protrusions; and a secondsurface on said foil element having protrusions positionally alternatingwith said first surface protrusions.
 21. A foil stiffening element as inclaim 20 wherein said protrusions have generally planar outer surfaces.22. A foil stiffening element comprising:a compliant foil element; afirst surface on said foil element having depressions; and a secondsurface on said foil element having depressions positionally alternatingwith said first surface depressions.
 23. In a foil stiffening elementfor use in a fluid bearing system having a plurality of bearing foils,the improvement comprising:means for providing a first operativeconfiguration of said foil stiffening element for providing damping bybending and a second operative configuration of said foil stiffeningelement for providing damping by compression.
 24. A foil stiffeningelement for use in a fluid bearing system having a plurality of bearingfoils, said element having a first operative configuration for providingdamping by bending and a second operative configuration for providingdamping by compression.
 25. In a compliant foil for use in a foilbearing system and comprising a generally arcuate-shaped, compliantmember including mounting means, the improvement comprising:a pluralityof alternating ridges and grooves along an inner surface of said foilelement extending in one direction from said mounting mean; andalternating ridges and grooves along an outer surface extending in saidone direction from said mounting means, each outer surface ridgepositionally corresponding to an inner surface groove.
 26. A compliantfoil as in claim 25 wherein said mounting means is intermediate the endsthereof, all of said ridges and grooves being positioned toward one ofsaid ends from said mounting means.